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Posted By Topic: Suspended Socket Outlets

OctaneOutlaw
Mar 17 2020 11:21

First time having to do one and I'm pretty happy with how it's gone but have I made the wrong decision by choosing to use 2.5mm flexible cord? It doesn't seem to fit into the PDL hanging outlet I have, I thought 2.5 would be the minimum size to use due to it supplying a socket outlet although I am aware there is an exception to this clause but didn't think it would apply here

Any advice or tips?

Also is a chain required? I've done one regardless but just curious

Basically I have a cable going into a j box on roof with a M20 gland drilled through the roof of the j box to grip the cable and then a chain hanging down for support, does this sound like something that would normally be done?


   

AlecK
Mar 17 2020 15:10

chain not a requirement.
As per Fig 4.8; the flex is installation wiring so same overcurrent protection requirements as the rest of the circuit. So a reduction in CCC would mean installing an additional device unless one of the exceptions applied.
   

MitchB
Mar 17 2020 15:19

Most j-boxes are made of pretty cheap brittle plastic, and are only held to their base by two little self tapping screws, are you happy it'll stand the test of time with that mechanical strain on it? Other than that it sounds fine.
   

OctaneOutlaw
Mar 17 2020 15:26

I understand that but I think it's table 3.3 saying that socket outlets should be supplied by 2.5mm minimum

And due to it being installation wiring as you said I assumed this would apply here

-------------

Yeah, fair points I've set up a chain to take the strain so I personally seem pretty happy with the j box and it's not taking the force of the cable, what other options would you use?
   

Cookies
Mar 17 2020 16:26

In theory the suspended socket outlet should only draw a maximum of 10amps anyway, appreciate someone can adapt this etc at the socket end itself but this is always the case.
The flex in comparison over a short distance has a much higher CCC compared to standard flat tps.

It wouldn’t be too much different to pendant lights with their downgraded flex sizing off the main feed size of the lighting circuit.

If your readings are well within the parameters I personally can’t see any issue with using a 1.5mm flex as the CCC would be capable of a 20amp supply and especially over a 2/3 metre drop.



   

OctaneOutlaw
Mar 17 2020 17:02

To an extent I agree with the fact that a item with a 10A plug should never exceed 10A but with multiboxs and adapters a sum of items could exceed 10A but I don't feel this is relevant unless you are trying to reference 2.5.3.4 (b)(ii) but this can't apply to socket outlets due to the reason above

I understand the CCC of a small conductor size would be suitable, looking at 3008 table 10 I assume a flexible cord installed as installation wiring and spaced in air (which I guess is what this would be) is 23A for 1.5mm and 18A for 1mm which the original circuit was on a 16A MCB so either would have been sufficient but as mentioned above it was the clause relating to socket outlet circuits requiring to be a minimum of 2.5mm that has thrown me off
   

Cookies
Mar 17 2020 17:41

Exception 1 takes care of that on table 3.3

But within reason I find for any situation like this (cable not terminating due to being too large) stand back and have a good look and sometimes it tells it’s own stor and makes sense in the end.
Obviously any single 10 amp outlet on any socket can be adapted to draw the full current of the circuit breaker protecting it.

   

Cookies
Mar 17 2020 17:49

Story sorry!
   

OctaneOutlaw
Mar 17 2020 18:17

I think it's just I thought that exception was more referring to lights or other small equipment connected via socket out and usually not in an area used for general use

Yeah, as soon as I encountered the issues is what sparked the question because it was obviously designed for a smaller sizes cable

It's ok, I appreciate the input, whether I choose to agree or disagree with something is up to me but any input is good because it makes you consider other points of views, so thanks for taking the time mate
   

Cookies
Mar 17 2020 18:33

Without going too much into it!
Exception 1 refers to using smaller conductors for supplying socket outlets from sub circuits as long as they can essentially handle the protective fuse current rating.

Probably more important is following using flexible cable as permanent wiring, there you can really go round in circles and then tie yourself in a knot.

   

AlecK
Mar 18 2020 12:20

for flex as installation wiring; the relevant table is Table 16 - which gives a CCC for 1.5 mm2 as 16 A.
The comparison with a luminaire isn't completely valid, as a luminaire is a known fixed load that so cannot impose an overload on the flex. Unlike a socket outlet.

Effectively this is a branch of a FSC, so if there's a reduction in CCC there has to be an overcurrent device for overload and for short circuit; unless an Exception applies. The fact of the socket being rated only 10 A makes NO difference to applying 2.5.1.3.

Yes Table 3.3 permits 1.5 to be used subject to conditions; but that also doesn't affect 2.5.1.3.
So would only have been compliant if protection rated 16 A, not more.

Flex used as installation wiring must be HD.
   

Cookies
Mar 18 2020 12:59

Then there is also exception (A) to 3.9.7.4 which says for pendant socket outlets the flex doesn’t have to be HD flex.
Like I’ve said above round in circles.

I would say HD flex may not actually fit into a pendant outlet either at 1.5mm?

In any case 1.5 tps is rated at 22 amps over 2-3 metres

Also it would be worth stepping the circuit down from 20 amp to 16amp at the fuseboard (if that was the case) and it was an issue rather than having an inaccessible fuse or mcb above a ceiling that would get forgotten about over time.

   

OctaneOutlaw
Mar 18 2020 13:01

I disagree sorry, if you look at the note below table 16

"3 The current-carrying capacity is based on a cable
maximum conductor operating temperature of 60°C in
order to limit the surface temperatures for the expected
use of such cables. Where flexible cords are used as
installation wiring, the current ratings are given in
Tables 4 to 15 and 17, see Clause 3.3.2."

So I still stand by table 10 being correct, the values in table 16 are for when they are not used as installation wiring

Also the comment "Flex used as installation wiring must be HD." is correct unless one of the exceptions is applied

Being a pendant socket ordinary duty is sufficient looking at "Exception: Flexible cords need not be of the heavy-duty type if—
(a) used for the connection of pendant socket-outlets;"
   

AlecK
Mar 18 2020 13:46

I accept both the Exception to 3.9.7.4 and that Table 10 applies
(can't be 100 % all the time; should have looked them up)
   

OctaneOutlaw
Mar 18 2020 13:57

Appreciate all the input regardless, these discussions are not about shunning other but more so that we can all benefit and become better at what we do

Next time I'll make sure to use a smaller flex size so I eliminate the issue I had
   

Cookies
Mar 18 2020 14:06

Agreed thats the great thing about this forum...... curious though round file or drill bit??😂
   

OctaneOutlaw
Mar 18 2020 15:29

Drill bit haha was still a squeeze thought
   

AlecK
Mar 18 2020 17:00

step drills can be very handy things